Detect current page of UIPageViewController

Question

I want to detect the current page in order to modify a button's title while the last page is showing and re-modify every time the user swipes back from the last to the second to last page.

Now these are my delegate methods and my array of ViewControllers:

lazy var VCArr: [UIViewController] = {
    let firstVC = self.storyboard!.instantiateViewController(withIdentifier: "FirstTutorialPage")
    let secondVC = self.storyboard!.instantiateViewController(withIdentifier: "SecondTutorialPage")
    let thirdVC = self.storyboard!.instantiateViewController(withIdentifier: "ThirdTutorialPage")
    let fourthVC = self.storyboard!.instantiateViewController(withIdentifier: "FourthTutorialPage")
    return [firstVC, secondVC, thirdVC, fourthVC]
}()

delegate methods

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

    guard let viewControllerIndex = self.VCArr.index(of: viewController) else {
        return nil
    }

    let previousIndex = viewControllerIndex - 1

    guard previousIndex >= 0 else {
        return nil
    }

    guard self.VCArr.count > previousIndex else {
        return nil
    }

    return self.VCArr[previousIndex]
}

func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
    guard let viewControllerIndex = self.VCArr.index(of: viewController) else {
        return nil
    }

    let nextIndex = viewControllerIndex + 1

    guard nextIndex < self.VCArr.count else {
        return nil
    }

    guard self.VCArr.count > nextIndex else {
        return nil
    }

    return self.VCArr[nextIndex]
}

Can someone help me detect with accuracy the last page shown? I tried some methods but everyone of them showed me the wrong index. Those methods detected the last index while showing the second to last page.

Thanks to all.

Answer 1

My solution consist in implementing the function pageViewController(_:didFinishAnimating:previousViewControllers:transitionCompleted:) of the UIPageViewControllerDelegate and doing the following:

if completed {
    if let currentViewController = pageViewController.viewControllers?.first,
    let index = pages.index(of: currentViewController) {
        currentIndex = index
    }
}

where pages is a property of my page view controller where I store all my view controllers to be presented and currentIndex is a property to keep track of the index of the current page (aka view controller) in order to use it in other parts of my code.